Answer
This is the correct method, because it will produce a solution with 1 L and 0.125 M $H_2SO_4$
Work Step by Step
1. Find the concentration after the dilution:
1 L = 1000 mL
$C_1 * V_1 = C_2 * V_2$
$6*20.8= C_2 *1000$
$125 = C_2 *1000$
$C_2 =0.125M$
After the dilution, the volume is equal to 1L.